Optical disc drive for performing read/write operations and optical disks

ABSTRACT

An optical disc drive compatible with optical discs of different types, for example, is provided. For focusing, through an optical system used in common with the different types of optical discs, a laser beam emitted from a selected one of a plurality of light sources disposed apart from each other radially of the optical disc, the optical system is moved radially of the optical disc correspondingly to the selection of the light source for emitting the laser light. Namely, it is possible to prevent the optical property from being deteriorated when a single optical pickup is used in common with such optical discs of different types.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical disc drive, and moreparticularly to an optical disc drive adapted to write data to, and/orread data from, any of optical discs different in format from eachother, such as compact disc (CD), digital video disc or digitalversatile disc (DVD), etc. According to the present invention, aplurality of light sources is disposed apart from each other radially ofsuch an optical disc and a laser light is emitted from one of the lightsources selected according to an optical disc loaded in the optical discdrive towards the optical disc and focused through a common opticalsystem for the different types of optical discs. Thus, a single opticalpickup can be used in common with such a plurality of optical discswithout any deterioration of the optical property.

[0003] 2. Description of the Related Art

[0004] The conventional optical disc drive or CD player is adapted toirradiate a laser beam from an optical pickup onto an informationrecording surface of a CD and process a detection result of a returnlight from the CD surface to read or reproduce a variety of datarecorded in the CD.

[0005] The conventional optical pickups include a type having a lightsource and photodetector disposed separately therein, and a type usingan optical integrated device consisting integrally of a light source andphotodetector. The U.S. Pat. Nos. 4,873,429 and 4,733,067 discloseexamples of the construction of the optical pickups of the latter type.This type of optical pickup can be designed more compact and have ahigher reliability.

[0006] It is considered that using such an optical integrated device tobuild the optical pickup also in a an optical disc drive for DVD, aso-called DVD player, for example, the DVD player can be designedcompact and simple. A DVD player designed to write data to, and/or readdata from, a CD as well will be very conveniently usable.

[0007] In this case, by forming an optical integrated device integrallyfrom a light source and photodetector for DVD and a light source andphotodetector for CD, an optical disc player capable of writing data to,and/or reading data from, both CD and DVD can be provided.

[0008] When the optical integrated device is constructed as in the aboveand an objective lens is used commonly used with both DVD and CD, eitherof the light source for DVD or that for CD will be disposed off theoptical axis of the objective lens. The laser beam emitted from thelight source thus disposed off the optical axis will be incidentobliquely to the objective lens. As a result, the obliquely incidentlaser beam will have an increased aberration and thus the opticalproperty will be deteriorated.

[0009] As defined in the standard, the pit depth in the compact disc(CD) is one eighth (λ/8) of the wavelength λ of the laser beamirradiated to the CD, while the pit depth in the DVD is one fourth (λ/4)of the wavelength λ of the laser beam irradiated to the DVD. Thus, inthe DVD player, it is difficult to detect a tracking error signal by thesimilar method to that for CD. Namely, tracking error signal has to beproduced by the so-called differential phase detection (DPD) method, forexample. In this DPD method, the laser diode as light source has to bedisposed in such a manner that the deflection plane of the laser beamwill be parallel or perpendicular to the scanning direction of the laserbeam.

[0010] For effective utilization of the internal space of the opticalintegrated device, the laser diode should desirably be disposed in sucha manner that the deflection plane of the laser beam will be parallel orperpendicular to the direction of the optical path of the laser beam.

[0011] However, when the laser beam deflection plane is directed as inthe above, the optical property of a read signal from the optical discwill be deteriorated.

OBJECT AND SUMMARY OF THE INVENTION

[0012] It is therefore an object of the present invention to overcomethe above-mentioned drawbacks of the prior art by providing an opticalpickup simply constructed and having a plurality of light sourcesselectively used to write data to, and/or read data from, an opticalrecording medium without any deterioration of optical property, and anoptical disc drive using the optical pickup.

[0013] According to the present invention, there is provided an opticaldisc drive adapted to read information from an optical disc by emittinga laser beam from a selected one of a plurality of light sourcesdisposed apart from each other radially of the optical disc and focusingthe laser beam on the optical disc, detecting a return light resultedfrom reflection of the laser beam at the optical disc and processing theresult of return light detection, the optical disc drive including:

[0014] a common optical system for irradiating the laser beam emittedfrom the selected one of the plurality of light sources to the opticaldisc; and

[0015] a moving means operative in response to an laser beam output fromthe selected light source to move all or a part of the optical systemradially of the optical disc.

[0016] According to the present invention, there is also provided anoptical pickup adapted to irradiate a laser beam to an optical recordingmedium, detect a return light from the optical recording medium andproviding a result of return light detection, the optical pickupincluding:

[0017] first and second light sources to emit the laser beams ofdifferent wavelengths, respectively;

[0018] a photodetector to detect the return light from the opticalrecording medium; and

[0019] an optical system to converge the laser beam emitted from aselected one of the first and second light sources and guide the returnlight from the optical recording medium to the photodetector;

[0020] the first and second light sources being disposed so that thedirections of the deformation, caused by the astigmatism, of thesectional shape of the laser beams emitted from the light sources willnearly coincide with each other; and

[0021] the optical system being adapted for common use with the laserbeams emitted from the first and second light sources, and including anastigmatism correcting means for common use with the laser beams emittedfrom the first and second light sources.

[0022] According to the present invention, there is also provided anoptical disc drive adapted to read information from an optical disc byemitting a laser beam from a selected one of a plurality of lightsources disposed apart from each other radially of the optical disc andfocusing the laser beam on the optical disc, detecting a return lightresulted from reflection of the laser beam at the optical disc andprocessing the result of return light detection, the optical disc driveincluding:

[0023] first and second light sources to emit the laser beams ofdifferent wavelengths, respectively;

[0024] a photodetector to detect the return light from the opticalrecording medium; and

[0025] an optical system to converge the laser beam emitted from aselected one of the first and second light sources and guide the returnlight from the optical recording medium to the photodetector;

[0026] the first and second light sources being disposed so that thedirections of the deformation, caused by the astigmatism, of thesectional shape of the laser beams emitted from the light sources willnearly coincide with each other; and

[0027] the optical system being adapted for common use with the laserbeams emitted from the first and second light sources, and including anastigmatism correcting means for common use with the laser beams emittedfrom the first and second light sources.

[0028] These objects and other objects, features and advantages of thepresent intention will become more apparent from the following detaileddescription of the preferred embodiments of the present invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a schematic diagram of the optical disc drive accordingto the present invention;

[0030]FIG. 2 is a plan view of an aperture of an optical pickup in FIG.1;

[0031]FIG. 3A is a plan view, and FIG. 3B is a sectional view, of theoptical integrated device included in the optical pickup in FIG. 2;

[0032]FIG. 4 is a plan view, enlarged in scale, of the light-incidentsurfaces of the optical integrated device in FIG. 3; and

[0033]FIG. 5 is a schematic diagram explaining how to process results oflight detection by the light-incident surfaces shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] (1) Overall Construction of an Embodiment

[0035] Referring now to FIG. 1, there is schematically illustrated anembodiment of the optical disc drive according to the present invention.The optical disc drive is generally indicated with a reference 1. InFIG. 1, first and second types of optical disc are shown. The firstoptical disc is a DVD indicated with a reference 2A and the secondoptical disc is a CD indicated with a reference 2B. The optical discdrive 1 reads data recorded in the DVD 2A and also data recorded in theCD 2B. These optical discs 2A and 2B are shown together in FIG. 1 forthe convenience of illustration and description of the optical discdrive 1.

[0036] The CD 2B is an optical disc from which recorded data can be readby irradiating a laser beam to an information recording surface of thedisc through a transparent substrate of 1.2 mm in thickness andprocessing a return light from the information recording surface. TheDVD 2A is an optical disc having information recorded therein with ahigher density than n the CD 2B and from which recorded data can be readby irradiating a laser beam to an information recording surface of thedisc through a transparent substrate of 0.6 mm in thickness andprocessing a return light from the information recording surface.

[0037] In this optical disc drive 1, an optical pickup 3 is disposed tobe movable radially of the optical disc by a predetermined sledmechanism. As shown in FIG. 1, the optical pickup 3 consists of anastigmatism correction plate 50, collimator lens 5, aperture 6 and anobjective lens 7. A laser beam emitted from an optical integrated device4 is irradiated to the optical disc 2A or 2B through the astigmatismcorrection plate 50, collimator lens 5, aperture 6 and objective lens 7.On the contrary, a return light from the optical disc 2A or 2B isincident upon the optical integrated device 4 through the objective lens7, aperture 6, collimator lens 5 and astigmatism correction plate 50.

[0038] The optical disc drive 1 processes a result of the detection ofthe return light by the optical integrated device 4 to produce atracking error signal, focus error signal and a read signal. The opticaldisc drive 1 moves the objective lens 7 based on the tracking and focuserror signals to control the tracking and focus, and processes the readsignal to reproduce data recorded in the optical disc 2A or 2B.

[0039] The optical integrated device 4 is formed from a light source andphotodetector for CD and a light source and photodetector for DVD bothintegrally disposed in one package. The optical integrated device 4 hastwo semiconductor laser diode chips for the light sources, respectively,disposed about 100 μm apart from each other radially of the optical disc2A or 2B. These semiconductor laser diode chips are selectively drivenunder the control of a system controller (not show) depending upon whichis currently used, the optical disc 2A or 2B. Thus, the opticalintegrated device 4 selectively emits a laser beam of a wavelengthcorresponding to the optical disc 2A or 2B towards the optical disc 2Aor 2B, and a return light from the optical disc 2A or 2B is detected bya corresponding photodetector.

[0040] The astigmatism correction plate 50 is a transparent parallelflat plate and it is disposed in the optical path of the laser beam andobliquely in relation to the optical axis of the laser beam. Theastigmatism correction plate 50 is equal in astigmatism to the laserbeam. Its gradient, thickness, etc. are selected to provide anastigmatism which will cancel that of the laser beam. Thus, theastigmatism correction plate 50 corrects the astigmatism of each oflaser beams different in wavelength from each other.

[0041] The collimator lens 5 converts the laser beam emitted from theoptical integrated device 4 and having passed through the astigmatismcorrection plate 50 to a nearly parallel beam. Note that the collimatorlens 5 is so disposed in relation to the optical integrated device 4that the optical axis thereof aligns with that of the DVD laser beam.Thus, the collimator lens 5 has the optical axis thereof not alignedwith the optical axis of the CD laser beam.

[0042] As shown in FIG. 2, the aperture 6 is a transparent plate with adielectric layer evaporated thereon and a circular opening formed in thecenter thereof Namely, the aperture 6 has the dielectric layer aroundthe central opening formed therein. The dielectric layer serves as afilter to selectively intercept a laser beam of 780 nm in wavelength forCD while allowing a laser light of 650 nm in wavelength for DVD topenetrate through it. Thus, the aperture 6 will shape the incident laserbeam for CD to be a beam having a diameter depending upon the diameterof the opening, while allowing the laser beam for DVD to pass throughthe aperture 6 with the shape thereof not changed at all. Note that theaperture 6 is so disposed that the center of the opening formed thereinwill nearly coincide with the optical axis of the CD laser beam.

[0043] The objective lens 7 is an aspheric plastic lens formed from atransparent resin by injecting molding. By selecting an appropriaterefractive index of the transparent resin and shape of the lens surface,the objective lens 7 is formed to focus the incident parallel laser beamfor DVD or CD onto the information recording surface of the optical disc2A or 2B. Thus, the objective lens 7 is formed as a so-called bifocallens for both the laser beams for DVD and CD, respectively.

[0044] Further, the objective lens 7 is movable by a tracking controlactuator 8 composed of a voice-coil motor radially of the optical disc2A or 2B so that tracking control can be done by driving the actuator 8correspondingly to a tracking error signal.

[0045] Also, the objective lens 7 is movable by a focus control actuator(not shown) along the optical axis of the laser beam so that focuscontrol can be done by driving the focus control actuatorcorrespondingly to a focus error signal.

[0046] When not forced by the tracking control actuator 8, the movableobjective lens 7 will be positioned for the optical axis thereof to bealigned with that of the DVD laser beam while the optical axis of theobjective lens 7 will not be aligned with that of the CD laser beam.When reading the CD 2B, the objective lens 7 is moved by the trackingcontrol actuator 8 radially of the CD 2B correspondingly to the spacingbetween the light sources in the optical integrated device 4, wherebythe optical property of the optical system is prevented from beingdeteriorated when reading the CD 2B.

[0047] The optical disc drive 1 further comprises a matrix calculationcircuit 9 as shown in FIG. 1. The matrix calculation circuit 9 providesa matrix calculation of a result of the light detection output from theoptical integrated device 4 to produce a tracking error signal TE whoselevel varies depending upon the magnitude of a tracking error, focuserror signal whose level varies depending upon the magnitude of a focuserror, and a read signal whose level varies depending upon the pittrain. The matrix calculation circuit 9 produces a tracking errorsignal, focus error signal and read signal for each of DVD and CD.

[0048] For the tracking control, the optical disc drive 1 furtherincludes a servo circuit 10 and drive circuit 11. The servo circuit 10produces a drive signal for use to enable a predetermined level of thetracking error signal TE, and the drive circuit 11 drives the actuator 8under the drive signal.

[0049] As shown in FIG. 1, the optical disc drive 1 further comprises aswitching circuit 12. For reading the CD 2B, the switching circuit 12will be closed under the control of the system controller to provide apredetermined offset voltage to the drive circuit 11 which in turn willadd the offset voltage to a drive signal provided from the servo circuit10, and thus drive the actuator 8. In this optical disc drive 1,tracking control is made with the objective lens 7 moved radially of theCD 2B.

[0050] (2) Construction of the Optical Integrated Device 4

[0051]FIG. 3A is a plan view, from the emitted direction of the laserbeam, of the optical integrated device 4, and FIG. 3B is a sectionalview, taken along the direction tangential to the circumference of theoptical disc 2A or 2B, of the optical integrated device 4. The opticalintegrated device 4 is constructed by disposing a prism 14, andsemiconductor laser diode chips 15A and 15B on a semiconductor substrate17 to form an optical system 16, putting the optical system 16 in apackage 18 and wiring it, and then sealing the package 18 with atransparent glass 19.

[0052] The semiconductor laser diode chips 15A and 15B are disposedapart by about 100 μm from each other radially of the optical disc 2A or2B and emit a laser beam having a wavelength of 650 nm for DVD and alaser beam having a wavelength 780 nm for CD, respectively, towards theprism 14. Also, the semiconductor laser diode chips 15A and 15B aredisposed for the deflection plane to be parallel or perpendicular to thescanning direction of the laser in the light-incident surface of theoptical disc 2A or 2B. Further, the semiconductor laser diode chips 15Aand 15B in pair are nearly equal in astigmatism to each other. They aredisposed so that the section of the laser beam will be deformed by theastigmatism in the same direction. Thus, in the optical disc drive 1,the single astigmatism correction plate 50 corrects the astigmatism ofeach of the laser beams emitted from the two light sources. When readinga DVD, a tracking error signal can be detected by the DPD (differentialphase detection) method.

[0053] The prism 14 is provided to separate the laser beam and returnlight from each other. It is formed to have a generally rectangularshape having a slope at one lateral side thereof. Thus, a laser beamemitted from the semiconductor laser diode chip 15A or 15B is reflectedat the slope of the prism 14 towards the collimator lens 5, and a returnlight having traveled reversely along the optical path of the laser beamand incident upon the prism 14 is guided inwardly of this slope.

[0054] At the prism 14, the return light incident upon the slope isincident upon the bottom of the prim 14. About 50% of the return lightis penetrated through the prism bottom while the remainder is reflectedtowards the top of the prims 14. The return light incident upon theprism top is reflected nearly 100% there towards the prism bottom andallowed to outgo through the prism bottom.

[0055] For the above reflection of the return light, the prism 14 has amirror surface formed by evaporation on the top thereof. Also the prims14 has a beam splitting surface formed on a portion of the bottomthereof at the slope side (will be referred to as “front side”hereinafter) and a light transmissive surface formed on a portion of thebottom thereof at the side away from the slope (will be referred to as“rear side” hereinafter) so that the ratio in amount between the returnlight allowed to outgo through the prism bottom at the front-sideportion and that allowed to outgo through the prism bottom at therear-side portion will be nearly 1:1. The beam splitting surface andlight-transmissive surface are formed by the similar evaporation to thatused in forming the mirror surface.

[0056] The semiconductor substrate 17 has light-incident surfaces 25Aand 26A for DVD and light-incident surfaces 25B and 26B for CD formed onportions, respectively, thereof upon which the return portion of thelaser beam for DVD and that of the laser beam for CD are incident fromthe prism 14.

[0057] The light-incident surfaces 25A and 25B are disposedcorrespondingly to the front-side portion of the prism 14, while thelight-incident surfaces 26A and 26B are disposed correspondingly to therear-side portion.

[0058]FIG. 4 is a plan view, partially enlarged in scale, of the lightdetection systems for CD and DVD, respectively, formed from theabove-mentioned light-incident surfaces of the optical integrated device4. For the optical integrated device 4, the directions of thesemiconductor laser diode chips 15A and 15B and size of the prism 14 areselected so that when the laser beam is just focused, a beam spotdefined on the semiconductor substrate 17 by the return light havingpassed through the prism 14 will be formed, at the rear-side portion,like a focal line, and at the front-side portion, like an ellipse havingthe major axis thereof directed perpendicularly to the extension of thefocal line at the rear-side portion.

[0059] The light-incident surfaces 25B and 26B for CD are formed side byside tangentially to the circumference of CD to have a general shape ofa rectangle, and each is divided radially of CD by a parting lineextending tangentially to the circumference of CD. Thus, when theoptical head is just on an intended track on a CD, each of thelight-incident surfaces 25B and 26B can detect a beam spot definedthereon and quartered radially of CD. Namely, a result of lightdetection by each of the quartered light-incident surfaces is providedas output. In FIG. 4, the outer light-incident surface divisions at thefront-side portion are indicated with references m and p, respectively,while the inner ones are indicated with references n and o,respectively. The outer light-incident surface divisions at therear-side portion are indicated with references q and t, respectively,while the inner ones are indicated with references r and s,respectively.

[0060] The light-incident surfaces 25A and 26A for DVD are formed sideby side tangentially to the circumference of the optical disc 2A in thesimilar manner to that for the light-incident surfaces 25B and 26B tohave a general shape of a rectangle. The light-incident surface 26A atthe rear-side portion is formed similarly to the light-incident surface26B at the rear-side portion for CD.

[0061] The light-incident surface 25A at the front-side portion isformed similarly to the light-incident surface 25B at the front-sideportion for CD, and further it is divided by two tangentially to thecircumference of the optical disc. Thus, the semiconductor substrate 17can produce a tracking error signal by the so-called differential phasedetection (DPD). As shown in FIG. 4, the outer and on-slopelight-incident surface divisions for DVD at the front-side portion areindicated with references a and d, respectively, and the inner andunder-slope light-incident surface divisions at the front-side portionare indicated with references b and c, respectively. Further, the outerand off-slope light-incident surface divisions at the front-side portionare indicated with references e and h, respectively, and the inner andoff-slope light-incident surface divisions at the front-side portion areindicated with references f and g, respectively. Also, the outerlight-incident surface divisions at the rear-side portion are indicatedwith references i and l, respectively, and the inner light-incidentsurface divisions at the rear-side portion are indicated with referencesj and k, respectively.

[0062] The semiconductor substrate 17 converts the results of lightdetection from the light-incident surface divisions a to t from currentto voltage, then calculates the converted signals and provide theresults of calculation to the matrix calculation circuit 9 where thecalculated signals will further be calculated to produce a trackingerror signal, focus error signal and a read signal.

[0063] When reading a CD, the results of light detection are processedas follows. Differences in light detection are detected between theinner and outer light-incident surface divisions of each of the front-and rear-side light-incident surfaces 25B and 26B, and then asubtraction between the differences is made between the front- andrear-side light surfaces 25B and 26B to produce a focus error signalexpressed by (m+p+r+s)−(n+o+q+t). Differences in light detection aredetected between the inner and outer circumferential light-incidentsurface divisions of each of the front- and rear-side light-incidentsurfaces 25B and 26B, and then a subtraction between the differences ismade between the front- and rear-side light surfaces 25B and 26B toproduce a tracking error signal expressed by (m+n+s+t)−(o+p+q+r). Thenall the results of light detection at the front- and rear-sidelight-incident surfaces 25B and 26B are added together to produce a readsignal expressed by (m+n+o+p+q+r+s+t).

[0064] When reading a DVD, the results of light detection are processedin the same manner as in the above for reading a CD to produce a focuserror signal expressed by (a+b+e+h+j+k)−(b+c+f+g+i+l) and a read signalexpressed by (a+b+c+d+e+f+g+h+i+j+k+l). On the other hand, forproduction of the tracking error signal TE for DVD, results of lightdetection are processed as follows. As shown in FIG. 5, results of lightdetection from two light-incident surfaces corresponding to the innerand outer circumferences of the optical disc 2A are added together byaddition circuits 42A to 42D for each of the groups of light-incidentsurface divisions defined in the direction of the light-incidentsurfaces 25A and 26A disposed side by side. Thus quantities of lightincident upon the inner and outer circumferential-side light-incidentsurface divisions are determined for each group. For each of the groups,results of light detection are compared in phase between the groups ofthe inner and outer circumferential-side light-incident surfacedivisions by phase comparison circuits 43A and 43B, and then addedtogether by an addition circuit 44 to produce a tracking error signalTE.

[0065] (3) Operation of the Embodiment

[0066] In the optical disc drive 1 constructed as having been describedin the foregoing with reference to FIG. 1, the optical pickup 3irradiates a laser beam to the optical disc 2A or 3B and detects areturn light from the optical disc, and a selected one of the signalprocessing circuits processes the result of return light detection,thereby reading information from the optical disc 2A or 2B.

[0067] More particularly, a laser beam is emitted from the opticalintegrated device 4 of the optical pickup 3 incorporated in the opticaldisc drive 1, converted to a nearly parallel beam by the collimator lens5, passed through the aperture 6, and guided to the objective lens 7which will focus the laser beam on an information recording surface ofthe optical disc 2A or 2B. A return light resulted from reflection ofthe laser beam at the information recording surface is passed throughthe objective lens 7 and incident upon the optical integrated device 4which provides results of return light detection as outputs.

[0068] In the optical disc drive 1, the tracking error signal TE isproduced by processing the results of return light detection as in theabove, and the objective lens 7 is moved by the servo circuit 10radially of the optical disc 2A or 2B until the tracking error signal TEgets a predetermined signal level. Namely, a tracking control is made.Similarly, a focus error signal is produced, and the objective lens 7 ismoved up and down until the focus error signal has a predeterminedlevel. This is the focus control according to the present invention.

[0069] When the optical disc (2A or 2B) loaded in the optical disc drive1 is a DVD (namely, 2A), one of the semiconductor laser diode chips 15Aand 15B disposed side by side in the optical integrated device 4radially of the optical disc 2A or 2B (see FIG. 3), that is, thesemiconductor laser diode chip 15A, is selected to emit a laser beamtowards the DVD 2A, and a return light from the DVD 2A is detected bythe light-incident surfaces 25A and 26A for DVD via the prism 14.

[0070] Since the optical pickup 3 is disposed so that the optical axesof the objective lens 7 and collimator lens 5 are generally aligned withthat of the DVD laser beam, the optical property can effectively beprevented from being deteriorated.

[0071] On the contrary, when the optical disc loaded in the optical discdrive 1 is CD (namely, 2B), the semiconductor laser diode chip 15B (seeFIG. 3) is selected to emit a laser beam towards the CD 2B, and a returnlight from the CD 2B is detected by the light-incident surfaces 25B and26B for CD via the prism 14.

[0072] In the optical disc drive 1, the switching circuit 12 is closed,so that an offset voltage is added to the drive signal supplied from theservo circuit 10 for moving the objective lens 7 over a predetermineddistance radially of the CD 2B (tracking control). Thus, in the opticaldisc drive 1, the aberration developed during read of the CD 2B can bereduced to prevent the optical property from being deteriorated.

[0073] The deteriorations of optical property were actually observedusing various signals produced by the matrix calculation circuit 9. Asthe results of the observation showed that when the objective lens 7 isnot moved at all, there took place in the tracking error signal TE adeviation of the S-characteristic from the one for the just tracking.When the collimator lens 5 had a focal distance of 23 mm and a distanceof 6.176 mm was provided between the collimator lens 5 and objectivelens 7, the deviation of the S-characteristic from the just-tracking onecould be prevented by moving the objective lens 7 towards thesemiconductor laser diode chip for CD.

[0074] The moving distance of the objective lens 7 varies in proportionto the ratio between the focal distance of the collimator lens 5 and thedistance between the collimator 5 and objective lens 7. By increasingthe distance between the collimator lens 5 and objective lens 7 incomparison with the focal distance of the collimator lens 5, theobjective lens 7 can be moved away from the semiconductor laser diodechip for CD, so that the deviation of the S-characteristic from thejust-tracking one can be prevented. Also, when the focal distance of thecollimator lens 5 is set equal to that the distance between thecollimator lens 5 and objective lens 7, it is possible to prevent theS-characteristic from deviating from the just-tracking one without thenecessity of moving the objective lens 7. In this case, however, thedesign of the objective lens 7 being a bifocal lens will be complicated.

[0075] (4) Effect of the Embodiment

[0076] To prevent the deterioration of the optical property by movingthe objective lens 7, the semiconductor laser diode chips 15A and 15Bare disposed side by side radially of the optical disc 2A or 2B in thepresent invention. So the tracking control actuator can be used toeasily move the objective lens 7. That is, according to the presentinvention, the optical pickup 3 may be designed simple for moving theobjective lens 7 to prevent the optical property from beingdeteriorated. The optical pickup 3 may be nearly the same inconstruction as for a compact disc.

[0077] Note that the laser beam for CD is focused on the compact disc 2Bwith the diameter thereof limited and numerical aperture reduced by theaperture 6.

[0078] The return light resulted from reflection of the laser irradiatedto an optical disc is incident upon the light-incident surfaces 25A and26A for DVD and those 25B and 26B for CD (as in FIG. 4), and the resultsof light detection from the light-incident surfaces 25A and 26B areprocessed depending upon whether the optical disc being played is 2A or2B, thereby reading the DVD or CD.

[0079] In the above optical disc drive 1, one of the semiconductor laserdiode chips 15A and 15B disposed apart from each other radially of theoptical disc is selected to emit a laser beam, and focused on theoptical disc 2A or 2B through the common optical system (including theelements 5, 6 and 7). At this time, the objective lens 7 forming a partof the optical system is moved radially of the optical disc foralignment with the laser beam emitted from the selected light source.Thus, when the single optical pickup 3 is used in common with theplurality of optical discs, it is possible to prevent the opticalproperty from being deteriorated.

[0080] In the foregoing, the prevent invention has been describedconcerning the embodiment in which only the objective lens is moved.However, the present invention is not limited to this embodiment but theentire optical system may be adapted to be movable.

[0081] Also, in the optical disc drive 1 according to the presentinvention, the astigmatism correction plate 50 made of a transparentparallel flat plate is disposed obliquely in the optical path of thelaser beam to correct the astigmatism of the laser beam emitted from aselected one of the light sources in reading the optical disc 2A or 2B.

[0082] For the astigmatism correction, there is disposed in the opticaldisc drive 1 the pair of the semiconductor laser diode chips 15A and 15Bnearly equal in astigmatism to each other in such a manner that thedeflection plane on the disc surface is parallel or perpendicular to thescanning direction of the laser beam and the sections of the laser beamsare deformed in a nearly same direction by the astigmatism. Therefore,the single astigmatism correction plate 50 can be used in common withthe two laser beams to correct the astigmatism of each of the laserbeams. Thus, the simple design of the optical disc drive 1 improves theoptical property.

[0083] As mentioned above, the semiconductor laser diode chips 15A and15B can be disposed in the optical disc drive 1 for the laser beamdeflection plane to be parallel or perpendicular to the scanningdirection of the laser beam, and the tracking error signal for DVD canbe produced by the DPD method. Also, since the internal space of theoptical integrated device 4 can effectively be utilized to enable acompact design of the optical integrated device 4.

[0084] Owing to the above-mentioned construction of the optical discdrive 1, a laser beam can be emitted from a selected one of thesemiconductor laser diode chips disposed apart from each other radiallyof the optical disc, and focused on the optical disc via the commonoptical system. In this light generation and guiding, the singleastigmatism correcting means can be used to correct the aberration ofthe laser beam. Thus, the simple design of the optical disc drive 1 willlead to an improvement of the optical property.

[0085] The present invention has been described in the foregoingconcerning the embodiment in which the transparent parallel flat plateis used as the astigmatism correcting means. However, the presentinvention is not limited to this embodiment, but the astigmatism may beformed from a cylindrical lens, hologram, Fresnel lens or the like. Whena coupling lens is used, the astigmatism correcting means may be formedon the coupling lens.

[0086] (5) Other Possible Embodiments

[0087] In the foregoing, the present invention has been describedconcerning the embodiment in which light-incident surfaces are formed inthe optical system for each of the types of optical discs. However, thepresent invention is not limited to this embodiment but all or a part ofthe optical system may be constructed for common use with the differenttypes of optical discs.

[0088] The present invention has been described in the foregoingconcerning the embodiment adapted to be compatible with both a CD andDVD. However, the present invention is not limited to this embodiment,but can be adapted to be compatible with both a CD and a recordablecompact disc such as CD-R.

[0089] The present invention has been described concerning theembodiment in which two different types of optical disc are read by thesingle optical pickup. However, the present invention is not limited tothis embodiment, but can be adapted to read more than two types ofoptical disc.

[0090] The present invention has been described in the foregoing as tothe embodiment in which the optical pickup is constructed from theoptical integrated device formed integrally from a light source andphotodetector. However, the present invention is not limited to thisembodiment, but it can be adapted such that the light source andphotodetector are disposed separately from each other.

[0091] As having been described in the foregoing, the optical disc driveaccording to the present invention is adapted such that when a laserbeam is emitted from a selected one of a plurality of light sourcesdisposed apart from each other radially of optical discs and focused onthe optical disc via a common optical system, the optical system ismoved radially of the optical disc correspondingly to the selected lightsource, thereby permitting to prevent the optical property from beingdeteriorated when one optical pickup is used in common with theplurality of optical discs.

[0092] Also according to the present invention, the single astigmatismcorrecting means is used to correct the aberration of more than onelaser beams, so that a simple construction of the optical disc driveassures an improved optical property when one of a plurality of lightsources is used to read one of a plurality of optical recording media.

What is claimed is:
 1. An optical disc drive adapted to read informationfrom an optical disc by emitting a laser beam from a selected one of aplurality of light sources disposed apart from each other radially ofthe optical disc and focusing the laser beam on the optical disc,detecting a return light resulted from reflection of the laser beam atthe optical disc and processing the result of return light detection,the optical disc drive comprising: a common optical system forirradiating the laser beam emitted from the selected one of theplurality of light sources to the optical disc; and a moving meansoperative in response to an laser beam output from the selected lightsource to move all or a part of the optical system radially of theoptical disc.
 2. The optical disc drive as set forth in claim 1,wherein: the optical system comprises an objective lens to focus thelaser beam on an information recording surface of the optical disc; themoving means is a tracking controlling means for controlling thetracking by moving the objective lens radially of the optical disc; andthe objective lens is moved radially of the optical disc in response tothe laser beam output from the selected light source.
 3. The opticaldisc drive as set forth in claim 1, wherein the plurality of lightsources and the photodetector for the return light are formed integrallywith each other.
 4. The optical disc drive as set forth in claim 1,wherein: the plurality of light sources includes a first light source toemit a laser beam of a first wavelength and a second light source toemit a laser beam of a second wavelength; and the moving means moves allor a part of the optical system in such a manner that when the laserbeam is emitted from the first light source, the optical axis of theoptical system coincides with the optical path of the first-wavelengthlaser beam and that when the laser beam is emitted from the second lightsource, the optical axis of the optical system coincides with theoptical path of the second-wavelength laser beam.
 5. The optical discdrive as set forth in claim 4, wherein the first and second lightsources are disposed in proximity to each other.
 6. The optical discdrive as set forth in claim 1, wherein the optical system is moved awayfrom the light source selected to emit a laser beam.
 7. The optical discdrive as set forth in claim 4, further comprising an astigmatismcorrecting means for common use with the laser beams emitted from thefirst and second light sources.
 8. An optical pickup adapted toirradiate a laser beam to an optical recording medium, detect a returnlight from the optical recording medium and providing a result of returnlight detection, the optical pickup comprising: first and second lightsources to emit the laser beams of different wavelengths, respectively;a photodetector to detect the return light from the optical recordingmedium; and an optical system to converge the laser beam emitted from aselected one of the first and second light sources and guide the returnlight from the optical recording medium to the photodetector; the firstand second light sources being disposed so that the directions of thedeformation, caused by the astigmatism, of the sectional shape of thelaser beams emitted from the light sources will nearly coincide witheach other; and the optical system being adapted for common use with thelaser beams emitted from the first and second light sources, andincluding an astigmatism correcting means for common use with the laserbeams emitted from the first and second light sources.
 9. The opticalpickup as set forth in claim 8, wherein the astigmatism correcting meansis a transparent parallel flat plate.
 10. The optical pickup as setforth in claim 8, wherein the first and second light sources are nearlyequal in astigmatism to each other.
 11. The optical pickup as set forthin claim 8, wherein the first and second light sources and thephotodetector are provided integrally in one package.
 12. The opticalpickup as set forth in claim 8, wherein the laser beams from the firstand second light sources are different in wavelength from each other.13. An optical disc drive adapted to read information from an opticaldisc by emitting a laser beam from a selected one of a plurality oflight sources disposed apart from each other radially of the opticaldisc and focusing the laser beam on the optical disc, detecting a returnlight resulted from reflection of the laser beam at the optical disc andprocessing the result of return light detection, the optical disc driveincluding: first and second light sources to emit the laser beams ofdifferent wavelengths, respectively; a photodetector to detect thereturn light from the optical recording medium; and an optical system toconverge the laser beam emitted from a selected one of the first andsecond light sources and guide the return light from the opticalrecording medium to the photodetector; the first and second lightsources being disposed so that the directions of the deformation, causedby the astigmatism, of the sectional shape of the laser beams emittedfrom the light sources will nearly coincide with each other; and theoptical system being adapted for common use with the laser beams emittedfrom the first and second light sources, and including an astigmatismcorrecting means for common use with the laser beams emitted from thefirst and second light sources.
 14. The optical disc drive as set forthin claim 13, wherein the astigmatism correcting means is a transparentparallel flat plate.
 15. The optical disc drive as set forth in claim13, wherein the first and second light sources are nearly equal inastigmatism to each other.
 16. The optical disc drive as set forth inclaim 13, wherein the first and second light sources and thephotodetector are provided integrally in one package.
 17. The opticaldisc drive as set forth in claim 13, wherein the photodetector has thelight-incident surface thereof divided in a first directioncorresponding to the scanning direction of the laser beam and in asecond direction perpendicular to the first direction and thus providesresults of light detection from these light-incident surface divisions.18. The optical disc drive as set forth in claim 13, wherein the firstand second light sources have the deflection surfaces thereof setparallel to the scanning direction of the laser beam or perpendicular tothe scanning direction.
 19. The optical disc drive as set forth in claim13, wherein the laser beams from the first and second light sources aredifferent in wavelength from each other.